1. Field of the Invention
This invention relates to an endless power transmission belt, also known as a V-belt. Such belts are widely used for automotive or industrial purposes and primarily comprised of an outer compression section, an inner tension section, and a load-carrying section disposed between the compression and tension sections. The load-carrying section utilizes longitudinally extending load-carrying cords imbedded in a cushion of polymeric material. For special purposes, such belts may also include other layers of material. Such belts may have a simple trapezoidal cross-section, or may be of the multi-rib type comprising a plurality of laterally speed trapezoidal sections formed in the compression section.
2. Prior Art Statement
The load-carrying cords utilized in the belts have evolved through the years from natural materials to rayon, nylon, or similar synthetic materials, to materials having a high modulus, such as aramid. These later materials are needed to create belts which are stronger, more stretch resistant, provide longer running times without losing their properties. Unfortunately, the elevated temperatures required to cure such belts cause significant expansion of the curing molds and the cords will tend to float in a random pattern unless some control is provided. This has been done in the past by forming a barrier of fabric or lateral cords (also known as tire cords). It has been found that the use of a single composite layer of fabric with a heavy rubber coating as a barrier results in an excessive splice thickness which will damage the cord when the belt is flexed. Typical of prior art constructions are shown in Waugh U.S. Pat. No. 3,478,613; Meadows U.S. Pat. No. 3,863,515; and Wolfe U.S. Pat. No. 4,022,070.
In order to control the location of the aramid load-carrying cords, it has been found that this can be accomplished by providing a fabric layer on the tension section outwardly of the load-carrying section. A second, discreet, rubber backing layer is disposed outwardly of the fabric layer to provide a pulley engaging surface. Despite the fact that this adds to the thickness of the cross-section of the belt, it succeeds in its purpose of preventing abrasion between the outer surface of the belt and the pulley. The result of the improvement is a belt having a greater belt life and a reduction in backside pulley wear, particularly in dusty environments such as in agricultural machinery. In addition, the backside coefficient of friction is greater than if fabric backing layers were to be used, and thus becomes important where the outer surface of the belt, which is the backing layer, engages a back side idler pulley in certain power transmission systems. The backing layer works in conjunction with an additional fabric layer, preferably rubber-impregnated, which is disposed between the backing layer and the load-carrying cords. A further advantage of this construction is the reduction in thickness of the splice, hereinafter sometimes referred to as splice thickness or simply splice, which is required in the fabric layer. In most constructions, the splice forces the strength cord to be misaligned in an axial direction, which is obviously undesirable. The combination of the fabric layer and the backing layer reduces the splice thickness to avoid the misalignment. The novel design is particularly useful in multiple rib belts, of the type shown in U.S. Pat. No. 4,139,406, issued to Richmond et al. It should be noted that backing layers having been used in other belt structures, such as designated by reference number 15 in U.S. Pat. No. 4,617,075 issued to Wetzel, et al., such layers were not intended for the purposes outlined above, but were used in the process for forming a toothed xe2x80x9ctimingxe2x80x9d belt. This patent also shows a layer 15A which is not fabric, but only a fiber reinforced rubber layer. Thus, the present structural arrangement creates unexpected results for creating a useful product.